The present invention relates generally to flywheel energy storage systems, and more particularly to devices, and methods for dissipating the heat energy developed during operation of such flywheel energy storage systems, which systems use a vacuum environment to reduce windage losses.
The ability of flywheels to accept and release energy over relatively short time periods has been known for many years and energy storage flywheels have been used, or proposed for use, in a variety of applications. Such proposed and actual use applications include motor vehicle applications and stand alone supplemental energy sources.
There is shown in FIG. 1 a simplified view of a conventional flywheel energy storage system 100 used for storing kinetic energy. The conventional flywheel system 100 includes a flywheel assembly 104 disposed in a flywheel housing 102. Further, the flywheel housing is configured and arranged so such flywheel assemblies 104 are run under vacuum, in order to avoid drag on the flywheel. The systems are evacuated with standard vacuum pumps, e.g. turbo pumps, and then sealed, preferably by pinching off and then fusing the end of a copper tube, thus forming an all metal seal, which is impervious even to argon. The materials that make up the flywheel system, however, may entrain or evolve substantial quantities of materials which may be released within the system when under a vacuum, thus causing a reduction of the vacuum during operation. To partially deal with that problem, a drag pump 106 for example, is incorporated into the flywheel assembly 104 for pumping gases from the flywheel housing 102 into a separate gas storage chamber 108.
The typical flywheel assembly 104 includes a flywheel, a shaft to which is secured the flywheel and one or more bearings or bearing assemblies that rotatably support the shaft. Traditionally, flywheels have been made of metal, e.g., high strength steel. More recently, flywheels have been fabricated using fiber composite materials, e.g., fiberglass or carbon wound with a resin binder, thereby making flywheels that are lighter in weight and capable of operating at higher speeds than the traditional metal flywheel assemblies operate.
Because the rotatable supporting of the rotating flywheel results in the production of heat energy in the bearings or bearing assemblies, as well as the production of heat energy by a number of other components of the conventional flywheel energy storage system 100 such as for example, the motor; the flywheel assembly 104 as well as the operational life of the flywheel energy storage system 100 is dependent upon the ability of the flywheel energy storage system to dissipate the heat energy being developed. One conventional technique to dissipate the heat energy involves the use of the supporting structure(s) for the flywheel, motor and the bearings or bearing assemblies as a thermal conduction path to conduct the heat energy of the bearings to the flywheel housing 102. The heat energy is thence communicated to the external environment or heat sink via the flywheel housing 102. If heat energy cannot be dissipated in the desired amounts to the heat sink, then the component temperature within the flywheel energy storage system 100 will not be maintained within optimal or desired limits thereby shorting the operational life of these components and thus reducing the operational availability of the flywheel energy storage system.
In some applications, such as when the flywheel energy storage system 100 is being used as an uninterruptible power supply (UPS), the flywheel energy storage system is located below grade (i.e., underground). In this way, a structural failure of the system or its components, no matter how unlikely, would be contained below grade. This arrangement also makes siting of the flywheel energy storage system 100 easier because the space above-ground does not have to be dedicated or reserved for the system. In addition, the end user""s cabinet or structure does not have to be designed around the physical space requirements for the flywheel energy storage system. The physical space requirements for a conventional flywheel energy storage system would involve for example, a space area about 3 ft. high and about 2 ft. in diameter, which may be larger than the typical dimensions of an end user""s cabinet.
One prior art technique for dissipating heat energy in such cases, involves providing a below grade structure, having a chamber in which is disposed the flywheel energy storage system 100. This structure also is configured so that the chamber is in fluid communication with the atmosphere, whereby heat energy generated by the flywheel energy storage system 100 is dissipated directly to atmosphere, which acts as the heat sink. This arrangement, however, requires the below grade structure to be configured or designed to include one or more above-grade or at grade openings that are sufficiently sized so there is a sufficient flow of air from within the chamber to the atmosphere and from atmosphere back into the chamber so a desired amount of heat energy is thereby dissipated. Such openings, however, also must be configured and designed to provide a barrier to infestation, such as by insects or animals, or provide a barrier so as the openings do not form an attractive nuisance to children or people. Further, the openings have to be designed to preclude environmental effects, such as those caused by the weather or other natural causes, from affecting the operation of the flywheel energy storage system or shortening its operational life. Also, the structures forming the openings would involve considerations of siting (e.g., visible nuisances), which negate in part some of the perceived advantages of locating the flywheel energy storage system 100 below grade.
In another technique the structure forms a closed chamber where the heat energy dissipated from the flywheel energy storage system 100 into the closed chamber is ultimately communicated to the ground or soil surrounding the structure (i.e., earth, ground or soil comprises the heat sink. Alternatively, the flywheel energy storage system 100 is disposed in the ground or soil without a surrounding structure so the heat energy is dissipated from the storage system directly to the surrounding earth, ground or soil. The earth, ground or soil conditions in some cases, however, do not provide good heat conductivity, consequently there is poor heat energy dissipation into the soil. In such a case, the desired or needed amounts of the heat energy being generated by the flywheel energy storage system cannot be effectively dissipated into the earth, ground or soil. Consequently, component temperatures cannot be maintained at optimal values, thereby shortening the expected operational life of the component and the mean-time-between-failure (MTBF) for the flywheel energy storage system. Thus, as a practical matter this technique is limited for only those cases where earth, ground or soil conditions are optimal for the dissipation of such heat energy. Consequently, in such cases, the chamber of the below grade structure is put into fluid communication with atmosphere as described above.
It thus would be desirable to provide a new device, apparatus or method for dissipating heat energy of a flywheel energy storage system (FESS) to the surrounding environment particularly when the capabilities of the heat sink proximal the FESS are not optimal to dissipate such heat energy. It would be particularly desirable to provide such a device, apparatus and method whereby at least some of the generated heat energy is communicated to a second heat sink, the second heat sink being remote from the FESS and having desirable heat transfer characteristics (e.g., heat transfer characteristics better than those of the heat sink proximal the FESS). It also would be particularly desirable to utilize such a second heat sink as a source of useable heat energy or to provide a mechanism for storing peak heat energy outputs that can be dissipated therefrom over time. Such heat energy dissipation devices or apparatuses preferably would be simple in construction and such methods would not require highly skilled users to utilize or install the device or apparatus.
The present invention features a device, system and method for dissipating at least some heat energy being generated by one or more heat generating components of a flywheel energy storage system. Such a device, system and method more particularly provides a mechanism by which such heat energy is dissipated to a heat sink that is remote from the location of the flywheel energy storage system and which heat sink is capable of continuously receiving and conducting such heat energy. In this way, the flywheel energy storage system (FESS) can be located at a location that is desirable from the standpoint of interfacing the FESS with other components to which the FESS provides energy, while at the same time providing a mechanism for transferring at least some heat energy from the FESS to a heat sink that is remote therefrom, which heat sink exhibits the desired heat transfer properties for dissipating heat energy. The amount of heat energy being dissipated to this remote heat sink is sufficient to maintain the operating temperature of the one or more FESS heat generating components at or below a given temperature value.
A heat dissipation method according to the present invention includes providing a heat pipe member, having first and second ends, and a heat dissipating member being thermally engaged with the heat pipe member second end and being configured to transfer heat energy therefrom. Such a heat pipe member includes a heat pipe, which is a heat transferring device having a sealed member, for example a sealed tubular member, with an inner lining of a wicklike capillary material and a small amount of a fluid in a partial vacuum. As is known to those skilled in the art, heat is absorbed at one end of the sealed member by vaporization of the fluid and this heat energy is released at the other end of the sealed member by condensation of the vapor. The condensate is returned to the xe2x80x9cone endxe2x80x9d via the capillary material so the absorption and release of heat energy is a continuing process.
The heat dissipation method also includes thermally engaging the heat pipe member first end to the flywheel energy storage system so that at least some heat energy being generated by the one or more FESS heat generating components, hereinafter the heat energy to be dissipated, is communicated to the first end and through the heat pipe member. Further, such method includes locating the heat dissipating member in a heat sink remote from the flywheel energy storage system, hereinafter remote heat sink. As indicated above, the remote heat sink is capable of receiving and conducting the heat energy to be dissipated from the heat dissipating member.
In specific embodiments, the heat sink in which the heat dissipating member is to be located is selected so the selected heat sink has different heat transfer characteristics from those of a heat sink that is proximal the flywheel energy storage system (i.e., a proximal heat sink). In more specific embodiments, the selected or remote heat sink comprises one of a fluid or a solid, where the fluid is one of a gas and a liquid. In yet an even more specific embodiment, the remote heat sink is the atmosphere, the earth or a body of water such as a pond, lake or the ocean. Even more specifically, the flywheel energy storage system is positioned so as to be below grade and the heat dissipating member is located above grade so that the heat energy to be dissipated is transferred from the heat dissipating member to atmosphere.
In other specific embodiments, thermally engaging the first end includes thermally engaging the heat pipe member first end to one of a portion of a housing or supporting structure of the flywheel energy storage system. The housing and/or supporting structure are thermally engaged with the one or more FESS heat generating components.
In alternative embodiments, a plurality of heat pipe members are provided, each of which is thermally coupled to the flywheel energy storage system. More particularly, the first end of each heat pipe member thermally engages one of the housing or supporting structure of the flywheel energy storage system. Alternatively, the heat pipe members are arranged so that at least one heat pipe member thermally engages the housing and/or at least another heat pipe member thermally engages the supporting structure. In yet another embodiment, a plurality of heat dissipating members are provided, one for each heat pipe member, where each of the heat pipe members thermally engages a corresponding one of the plurality of heat dissipating members.
There also is featured a heat dissipation device for a flywheel energy storage system including a heat pipe member having a first end and second end, a heat dissipating member thermally engaged to the heat pipe member second end and being configured to transfer heat energy therefrom. The heat pipe member first end is configured and arranged so as to thermally engage a portion of the flywheel energy storage system such that at least a portion of heat energy generated by one or more components thereof, the heat energy to be dissipated, is transferred to the heat pipe member and communicated from the first end to the second end. Further, a length of the heat pipe member is set so that the heat dissipating member is located in a heat sink that is remote from the flywheel energy storage system, hereinafter remote heat sink, the remote heat sink being capable of receiving and conducting the heat energy to be dissipated from the heat dissipating member. As to the characteristics of the remote heat sink, and other features of the heat dissipation device, reference shall be made to the foregoing discussion regarding the heat dissipation method of the present invention.
In alternative embodiments, the heat dissipation device includes a plurality of heat pipe members, where the first ends thereof thermally engage the flywheel energy storage system as described above. In more particular embodiments, the first end of each heat pipe member is configured so as to thermally engage one of a housing or supporting structure of the FESS, which housing or supporting structure is thermally coupled to the one or more heat generating components. In yet another particular embodiment, the heat dissipation device includes a plurality of heat dissipating members, one for each heat pipe member, where each heat pipe member thermally engages a corresponding one of the plurality of heat dissipating members.
Also featured is a flywheel energy storage system (FESS) including one or more heat generating components and a heat dissipation device as described above that is thermally coupled to the one or more heat generating components and the remote heat sink. In more particular embodiments, the FESS further includes one of a housing or supporting structure that is thermally coupled to the one or more heat generating components. In these particular embodiments, the heat dissipation device is thermally coupled to one of, or both of, the housing and the supporting structure. Alternatively, the FESS includes a plurality of heat dissipation devices, each being thermally coupled to the one or more heat generating components and the remote heat sink. In yet other embodiments, the heat dissipation device comprises a plurality of heat pipe members alone or in combination with a plurality of hest dissipating devices as described above.
Other aspects and embodiments of the invention are discussed below.